Summertime partitioning and budget of NO_y compounds in the troposphere over Alaska and Canada: ABLE 3B

As part of NASA's Arctic Boundary Layer Expedition 3A and 3B field measurement programs, measurements of NO x , HNO 3 , PAN, PPN, and NO y were made in the middle to lower troposphere over Alaska and Canada during the summers of 1988 and 1990. These measurements are used to assess the degree of closure within the reactive odd nitrogen (N x O y ) budget through the comparison of the values of NO y measured with a catalytic convertor to the sum of individually measured NO y (i) compounds (i.e., ΣNO y (i) = NO x + HNO 3 + PAN + PPN). Significant differences were observed between the various study regions. In the lower 6 km of the troposphere over Alaska and the Hudson Bay lowlands of Canada a significant fraction of the NO y budget (30 to 60%) could not be accounted for by the measured ΣNO y (i). This deficit in the NO y budget is about 100 to 200 parts per trillion by volume (pptv) in the lower troposphere (0.15 to 3 km) and about 200 to 400 pptv in the middle free troposphere (3 to 6.2 km). Conversely, the NO y budget in the northern Labrador and Quebec regions of Canada is almost totally accounted for within the combined measurement uncertainties of NO y and the various NO y (i) compounds. A substantial portion of the NO y budget's “missing compounds” appears to be coupled to the photochemical and/or dynamical parameters influencing the tropospheric oxidative potential over these regions. A combination of factors are suggested as the causes for the variability observed in the NO y budget. In addition, the apparent stability of compounds represented by the NO y budget deficit in the lower‐altitude range questions the ability of these compounds to participate as reversible reservoirs for“active”odd nitrogen and suggest that some portion of the NO y budget may consist of relatively unreactive nitrogen‐containing compounds.